f(x) = COS(x)·(2 + SIN(x)^2)
f'(x) = - SIN(x)·(2 + SIN(x)^2) + COS(x)·(2·SIN(x)·COS(x))
f'(x) = - 2·SIN(x) - SIN(x)^3 + 2·SIN(x)·COS(x)^2
f'(x) = SIN(x)·(- 2 - SIN(x)^2 + 2·COS(x)^2)
f'(x) = SIN(x)·(- 2 - SIN(x)^2 + 2·(1 - SIN(x)^2))
f'(x) = SIN(x)·(- 2 - SIN(x)^2 + 2 - 2·SIN(x)^2)
f'(x) = SIN(x)·(- 3·SIN(x)^2)
f'(x) = - 3·SIN(x)^3